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My 2000 NB8a has all the symptoms of a coil pack issue. Rough idle with lower revs than normal. Slight smell of petrol. No power when accelerating. Cone filter is louder with more intake noise. Air bag light stays on ??
Problem is it seems to come and go.
Starts fine and goes or starts rough.
No problem starting.
Have not dríven it far. Maybe 300 metres and turned for home.
Where do I start ? Is it an electrical issue ? I'm no good with electrickary but want to keep this DIY.
Any help appreciated.

Most coil pack failures are heat sensitive, and fail after a little while driving. See if you can prompt the fault by flexing the harness where it connects to each coil, this is also a regular failure point as the harness points directly up, before bending 180deg to plug in downward. If you can get it to fail and continue to idle roughly, you can disconnect one coil at a time to determine which one is failing.

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If you have a mate with the same model do a coil swap. Coil can also be tested by Ignition service people - it should not cost anything- you can remove it and present it to them- check your area for Ignition co's. Many people just start changing things hoping they get the right result. A garage may be able to trouble shoot by doing some tests. Essentially the MX5 is a regular car most vehicles have the same electronic sensors. DIY goes so far- many people realise that they dont have the equipment and know how to fix modern engines. The coil swap test you can do and the suggestions others said about just removing a plug lead also can be useful and easy to do.

Start with new plugs and leads.....;)

Turns out #3 spark plug well had oil in it from a leaky tappet cover gasket.
New gasket, plugs and leads and she'd purring like a sewing machine again. Power delivery is also a lot smoother.
Happy days.